Storage-cavern apparatus and process for treatment of the displacing water



Dec. wel T966 c. W. VARVEL.

STORAGE-CAVERN APPARATUS AND PROCESS FOR TREATMENT OF THE DISPLACING WATER Filed Jan. 14, 1964 loco. om: zmm

INVENTOR. C lW. VARVEL NNHWHVU mzdml OP PUDDOma A 7' TORNEVS United States Patent O 3,289,416 STORAGE-CAVERN APPARATUS AND PROCESS FOR TREATMENT OF THE DISPLACING WATER Charles W. Varvel, Bartlesville, Okla., assignor to Phillips Petroleum Company, a corporation of Delaware Filed Jan. 14, 1964, Ser. No. 337,676 13 Claims. (Cl. 61.S)

This invention relates to a process and apparatus for use in the underground storage of fluids. Liquids and liquefied gases are frequently stored in subterranean caverns such as salt caverns. Liq-ueed petroleum gases (LPG) are conveniently stored in this type of cavern. Such gases as produced in a plant are normally very low in both water and oxygen and can be stored in steel tanks or transported in pipe lines without causing corrosion difficulties, However, the practice of storing LPG in salt caverns over water has changed this situation and caused a serious corrosion problem.

The water used for displacing propane, for example, is often stored in open ponds and tanks or obtained from other surface sources which contain CO2 and O2 in equilibrium with the water at atmospheric temperature. When this water enters the lcavern at .the elevated temperature of the earth at cavern level, usually 100 F. and higher, some of this CO2 and O2 is liberated to the Stored propane or LPG, 4carrying with it water vapor and causing the stored liquid to become -corrosive to the pipe lines and other metal handling facilities. This has been found to be the cause of the corrosion difficulty in connection with the storage and dispensing of LPG in subterranean caverns.

This invention is concerned with a process and arrangement of apparatus for overcoming the foregoing problem.

Accordingly, it is an object of the invention to provide a process and arrangement of apparatus for storing and dispensing fluids in subterranean Caverns with a minimum of corrosion difficulties in the dispensing of the stored uid. Another object is the reduction or elimination of corrosion in the dispensing of LPG and other liquid hydrocarbons from subterranean storage caverns of substantial depth. It is also an object of the invention to improve the economy of a storage cavern system. Other objects of the invention will 'become apparent upon consideration of the accompanying disclosure.

A broad aspect of the invention comprises heating the water utilized in displacing the liquid from the cavern into the dispensing line and stripping the heated water in a simple tower with a suitable stripping gas to remove the CO2 and O2 which normally would be liberated at that temperature and a portion of the remaining dissolved CO2 and O2, depending upon the efficiency of the column. This treatment of the displacing water has a two-fold effect of drastically reducing the amount of CO2 and O2 in the dispensed liquid and of limiting the transfer of water Ibetween the two layers of liquid in the storage cavern to the normal diffusion at the interface, thus reducing corrosion in handling facilities. It is advantageous and convenient to utilize a portion of the dispensed vaporized liquid from the storage cavern as the stripping gas. To illustrate, when storing LPG in a subterranean cavern, a small stream of the dispensed liquefied gas is ,passed to the stripping coluimn as the stripping gas. Another feature of the process is the heating of the displacing water in a gas-tired heater, at least to effect the final heating, and utilizing the off-gas from the strip ping column (LPG) as the fuel foi the gas-fired heater.

Another aspect of the invention comprises heat exchanging the dispensed liquid in the delivery line with the displacing water -prior to the final heating of this water before passage to the stripping tower. Since the cavern ice temperature in deep caverns is higher than :atmospheric temperature, a substantial amount of heat can be trans- .ferred from the displaced fluid from the storage cavern as the water is injected thereto as the displacing medium.

A more complete understanding of the invention may -be obtained by reference to the accompanying schematic drawing which illustrates a preferred arrangement of apparatus in association with a storage cavern for electing the invention.

Referring to the drawing a subterranean storage cavern 10 contains a body of water 12 in its lower section and LPG 14 in its upper section with an interface 16 be# tween the two bodies of liquid. A displacing line 18 leads to the vicinity of the bottom of the cavern and a stored fluid line 20 connects with the upper section of the cavern through a head 22 at ground level. Line 20 passes through an indirect heat exchanger 24 and through a filter 26 for removing water from the dispensed fluid. Bypass lines 28 and 30 are provided around heat exchanger 24 and filter 26, respectively. A supply line 32 for feeding liquid to be stored in the cavern connects with line 20 at any suitable position or with a separate line (not shown) leading through head 22, as desired.

A water supply line 34 for the displacing uid to be injected into the cavern through line 18 passes through heat exchanger 24 and through a suitable heater 36, connecting with the inlet 38 of a stripping tower 40. Stripping tower 40 is a conventional piece of apparatus which provides means for effecting vapor-liquid contacting. Stripping gas is supplied to a lower section of the column through line 42 which may conveniently connect with dispensed Huid line 20. Efuent gas from the top of the tower is Vadvantageously passed through line 44 to furnace 36 as fuel thereto and is supplemented with fuel from line 46 when required. The supply of stripping gas taken from line 20 and passing through line 42 passes through heat exchanger 48 where it is vaporized in indirect heat exchange with water passing through line 18 from the .bottom of tower 40 to cavern 10.

Flow of stripping gas through line 42 is controlled by a motor valve 50 therein which is operatively controlled 'by temperature controller 52 which is in turn sensitive to the temperature in line 38. In this manner, when the temperature in line 38 falls below a desired predetermined temperature for which temperature controller 52 is set, this instrument opens motor valve 50 farther so as to pass more stripping gas to tower 40 which is then b-urner in furnace 36 to supply additional heat and heat the water to a higher temperature.

It is also feasible to use other stripping gas in tower 40 than the stored gas. lt is also within the scope of the invention to supply all of the fuel gas required in furnace 36 from supply line 46. In the event stripping gas is used in tower 14 which is not combustible, the off-gas from the tower is vented through line 54.

In the system illustrated, a substantial part. of the heat needed, such as 25-30 percent, is obtained in heat exchanger 24 from the dispensed stored liquid. The balance of the heat is provided by the stored fluid serving as stripping gas coming from line 42. Depending upon the temperatures involved this stripping -gas can amount to as' much as 0.5 weight percent of the LPG (or other stored liquid) being transferred through line 20. If other sources of heat are available and are less expensive, they may be used as the heat source in furnace 36.

Since the temperature of the LPG or other stored liquid is reduced upon passage through heat exchanger 24, any free water formed in the stream is removed in filter 26 in conventional manner,

The water feed to the cavern 10 through line 18 is heated to at least the temperature of the cavern and, preferably, to a temperature -107 above cavern temperature. Heating the displacing water to this temperature and stripping same in tower 40 prevents any material transfer of CO2 or O2 from the mass of water 12 to the mass of stored liquid 14 in cavern 10 and thereby prevents or greatly reduces corrosion problem in line and in other metal-handling equipment downstream of this line.

Certain modifications of the invention will become apparent to those skilled in the art and the illustrative details disclosed are not to be construed as imposing unnecessary limitations on the invention.

I claim:

1. In a process for handling liquefied stored gas in an underground cavern over water wherein the gas is displaced frorn the cavern into metal conveying equipment such as a pipeline or metal cylinders, by water which is saturated with at least one gas of the group consisting of CO2 or O2 at a temperature lower than reservoir temperature so that upon displacing said liquefied gas with said water, the saturating gas diffuses into said liquefied gas at the water-gas interface and causes corrosion in said equipment, the improvement comprising:

(1) heating said water to a temperature at least as high as cavern temperature;

(2) passing the heated water of step (1) thru a stripping zone in countercurrent flow with vaporized liquefied gas as stripping gas; and

(3) passing the stripped water from step (2) into said cavern to displace stored liquefied gas therefrom.

2. The process of claim 1 wherein the heating of step (l) comprises passing a stream of said water in indirect heat exchange with the displaced liquefied gas and thereafter further heating said stream; and a portion of the displaced gas is used as the stripping gas of step (2).

3. The process of claim 2 wherein said liquefied gas is LPG.

4. The process of claim 2 wherein said liquefied gas is LPG and the effluent gas from the stripping zone is burned to complete the heating of the water stream.

5. A process comprising the steps of:

( 1) displacing a stream of stored liquefied combustible gas from a subterranean storage cavern wherein the storage ltemperature is substantially above atmospheric temperature thru a delivery line by forcing a stream of water into said cavern thru a line leading to a lower level thereof;

(2) before forcing the stream of water of step (1) into said cavern,

(a) passing said stream in indirect heat exchange with the stream of displaced liquefied gas to heat the displacing water;

(b) further heating the effluent stream of water of (a) to at least cavern temperature; and

(c) passing the heated stream from (b) thru a stripping zone in countercurrent contact with a stripping gas to remove impurities including CO5,l and O2 from the water.

6. The process of claim 5 wherein the efliuent stripping gas from (2) (c) is combustible and is 'burned to effect the heating (2) (b).

7. The process of claim 6 wherein the cooled stream of liquefied gas from step (2) (a) is passed thru a filtering zone to remove water therefrom.

8. The process of claim 5 wherein dispensed liquefied gas from said cavern is vaporized in indirect heat exchange with the effluent hot water from step (2)(c), the vaporized stream is utilized as the stripping gas of (2) (c), and the effluent stripping gas from (2)(c) is burned in the heating of step (2) (b).

9. In combination with a fluid storage cavern having a stored iiuid line leading into the upper section thereof and a displacing line leading into the lower section thereof,

(1) a water line leading from an aboveground source of water thru an indirect heat exchanger in said fluid line;

(2) a heater in the water line of (1) downstream of the exchanger therein;

(3) a stripping tower having an inlet in its upper section connected with said water line downstream of the heater of (2), an outlet in its top for gas, an inlet in its lower section for stripping gas, and an outlet in its lower section for stripped Water; and

(4) a line leading from the water outlet of (3) to said displacing line.

10. The combination of claim 9 wherein the inlet (3) for stripping gas connects with said stored iiuid line.

11. The combination of claim 9 wherein the inlet (3) for stripping gas connects with said stored fluid line, the heater of (2) is gas-fired, and the gas outlet of (3) is connected with the heater of (2).

12. The apparatus of claim 9 including a vaporizer in the line of (4), a line connecting the inlet (3) for stripping gas with said stored fluid line passing thru said vaporizer for indirect heat exchange with the heated water.

13. In combination with a fiuid storage cavern having a stored fluid line leading into the upper section thereof and a displacing line leading into the lower section thereof,

(1) a water line leading from an aboveground source of water having an indirect heat exchanger therein, said stored iiuid line passing thru said exchanger;

(2) a gas-fired heater in the water line of (l) downstream of the exchanger therein;

(3) a stripping tower having an inlet in an upper section for water to be stripped connected with the water line of (1) downstream of the heater of (2)7, a gas outlet in an upper section, a stripping gas inlet in a lower section, and a water outlet in a lower section;

(4) a line connecting the water outlet of (3) with said displacing line having a heat exchanger therein;

(5) a valved line connecting said stored fluid line with the stripping gas inlet of (3); and

(6) a line connecting the gas outlet of (3) with the burner of the heater of (2) for supplying fuel gas thereto.

No references cited.

EARL I WII MER, Primary Examiner. 

1. IN A PROCESS FOR HANDLING LIQUEFIED STORED GAS IN AN UNDERGROUND CAVERN OVER WATER WHEREIN THE GAS IS DISPLACED FROM THE CAVERN INTO METAL CONVEYING EQUIPMENT SUCH AS A PIPELINE OR METAL CYLINDERS, BY WATER WHICH IS SATURATED WITH AT LEAST ONE GAS OF THE GROUP CONSISTING OF CO2 OR O2 AT A TEMPERATURE LOWER THAN RESERVOIR TEMPERATURE SO THAT UPON DISPLACING SAID LIQUEFIED SAID WATER, THE SATURATING GAS DIFFUSES INTO SAID LIQUEFIED GAS AT THE WATER-GAS INTERFACE AND CAUSES CORROSION IN SAID EQUIPMENT, THE IMPROVEMENT COMPRISING: (1) HEATING SAID WATER TO A TEMPERATURE AT LEAST AS HIGH AS CAVERN TEMPERATURE; (2) PASSING THE HEATED WATER OF STEP (1) THRU A STRIPPING ZONE IN COUNTERCURRENT FLOW WITH VAPORIZED LIQUEFIED GAS AS STRIPPING GAS; AND (3) PASSING THE STRIPPED WATER FROM STEP (2) INTO SAID CAVERN TO DISPLACE STORED LIQUEFIED GAS THEREFROM. 